Apparatus for production of uranium



Fell 26, 1963 D. R. ALLEN r- TAL 3,079,324

APPARATUS FOR PRODUCTION OF URANIUM Filed June 30, 1958 2 Sheets-Sheet l TTORNEY 2 Sheets-Sheet 2 Feb. 26, 1963 D. R. ALLEN ETAL APPARATUS FOR PRODUCTION OF URANIUM Filed June 30, 1958 INVENTORS. Doria/dR. l//en nne'e 5. ,Q//en ATTORNEY United States idatent 3,679,324 APPAQATUS FR PRGDUCTEGN F UlitANl-"Ull'i Donald R. Allen and Annette Allen, Lake Jackson, Tex., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Enne 3l), i953, Ser. No. 745,715 S Claims. (Si. ml-246) The invention pertains to the production of uranium metal by the electrolysis of a uranium salt in a fused salt bath. More particularly, it pertains to an improved cell and electrolyte for use in such production.

The methods for the production of uranium presently employed fall generally into four types:

(l) Reduction of uranium oxides with carbon;

(2) Reduction of the uranium oxides with aluminum, Ca, Mg, or a hydride;

(3) Reduction of uranium halides with an alkali metal or an alkaline earth metal, and

(4) Electrolytic decomposition of uranium halides.

Uranium has wide general utility. lt is a valuable metal in metallurgy, forming such intermetallic compounds as UAl5, UNi, UleNi, UBig, and USntn and forming useful alloys with a number of metals such as Cr, Ca, W, Mg, Mo, Ti, and Zn. Uranium forms chemical compounds of importance among which are the hydride, deuteride, boride, carbide, silicide, nitride, phosphide, arsenide, hydrogridc, halide, and sulfide. lt forms the complex ions U02 and which react to form such salts as UO2F2 and UOC12, respectively.

The more extensive use of titanium, however, is due to its unique position in the provision of solid fuel for atomic reactors. Methods of producing uranium metal electrolytically appear to otter certain advantages over other methods. The production of uranium by electrolysis of uranium salts is Vdescribed in US. Patents 2,591,- 792; 2,690,421; and 2,781,304. U.S. Patent 2,773,825 particularly describes an improved cell for the electrolytic production of uranium metal. Among the known methods are the electrolysis of fused mixtures of halide salts containing Ul; electrolysis of from 5 to l5 percent KUF5, UF4, or UCL, in a fused bath consisting of 80 percent CaClZ and 2O percent NaCl employing an Mo metal cathode; and electrolysis of a fused halide bath containing a uranium halide in the presence of uranium carbides.

ri`he known means for producing uranium to meet the increased demand due to its use in the production of atomic energy, are not fully satisfactory. Although electrolytic production is favored, the present cells and the electrolyte used do not provide smooth and efficient decomposition of uranium salts and the recovery of the metal.

Consequently, there is a need for an improved electrolytic cell for the production of uranium metal.

Principal objects of the invention, therefore, are to provide an improved cell and electrolyte for the electrolysis of uranium salts to produce uranium metal. Another object is to provide a cell for the production of chlorine gas as a byproduct in the production of uranium. A further object is to provide a means for the production of uranium metal and chlorine gas in a continuous process whereby spent electrolyte is gradually withdrawn from the cell and make-up electroryte is added periodically or moreor-less continuously to tie body of the electrolyte,

The means for the accomplishment of these and related obiects will he made clear by the following description of the invention when read with reference to the annexed drawing.

ln the drawing,

FIGURE l is an elevational view largely in section of one embodiment of the cell of the invention.

FIGURE 2 is an elevational view largely in section of another embodiment of the cell of the invention.

FlGURE 3 is an isometric view of one embodiment of an inner anode member of the cell of either FIGURE 1 or 2 having slots therein.

FIGURE 4 is an elevational view largely in section of a cell of the invention having a slotted inner anode member wherein the slots are sloped upwardly toward an outer anode member.

FIGURE 5 is an enlarged view of a fragmentary portion of the inner anode member shown in FIGURE 4.

ln the drawing similar parts are designated by the same number in the different figures so `that the drawing may be more readily interprete-d.

Referring to the drawing in greater detail and especially to FIGURE l, there is shown furnace setting E forming heating chamber 9 provided with gas burner lil and exhaust l2 for combustion gases. Suspended within 8 by means of shoulder 14 is electrolyte container lo of carbon delined by impervious Hoor ll, impervious cylindrical sidewall 2G, and cover' 22. Steel sheath 19 protects carbon bottom 13 and sidewall Z0 from being damaged by heat from lll. Sidewall Ztl together with bottom 13 also serves as an outer anode member of the cell. Electrically insulating gaskets l5 are provided between shoulders i4 and both the metal wall of furnace setting 8 and cover 22. in FIGURE l. Spaced inwardly from sidewall 2li is cylindrical inner carlton anode member 24 which is integrally attached at the top thereof to the top of sidewall 2@ by horizontal annular graphite plate 26. Anode member 24, which extends downwardly toward but does not reach bottom 1S, is porous, perforate, or slotted to permit fluid passage therethrough. Inner anode member 24 usually extends to Iwithin 6.25 to l inch of bottom 1S. Anolyte compartment 27 is the annular compartment of chamber lo formed between 2t) and 24. Catholyte compartment 2S is that central portion of chamber 16 defined by inner anode member 24.

Subtended centrally in compartment 23 by means of electrically insulated radiating arms 30 is metal cathode 32 which extends downwardly through an opening provided therefor in cover 22 toward but short of contact with bottom 18. Any conducting material may be used which has a sufficiently high melting point and is unreactive with the bath or products produced. Electrically insulating packing 33 provides a tight t between cathode 32 and the opening in cover 22 through which it passes.

Electrical line 34 is attached to shoulder f4 of chamber lo and leads to the positive terminal of a source of DC. Electrical line 36 is attached to cathode 32 and leads to the negative terminal of the source of DC.

Outlet pipe 3S, leading from anolyte compartment 27,-

permits egress of gases, eg., chlorine, formed during electrolysis. lt is inserted through a hole provide therefor in annular plate 26 and cover 22. Electrical insulating gasket 39 is provided about line 3S as it passes through the hole in plate 26.

Inert gas line 4d containing valve 42 provides a means for blanketing the zone in the cell a'oove electrolyte 43 with an inert or a relatively inactive gas, eg., argon or nitrogen, if desired. Vent line i4 containing valve do provides a means for venting the zone above the electrolyte.

A modification of the cell of the invention particularly suitable for continuous operation is shown in FIGURE 2 wherein outlet Sil is provided in the side of the cell at the electrolyte level for both spent electrolyte and chlorine gas. Feed opening S2 having closing plate S4 thereover is shown in cover 22 to provide a means for supplying fresh feed into the electrolyte chamber.

FIGURE 3 is a view of an inne-r cylindrical anode connection with the outer anode member.

member with a portion of the top annular plate 26 attached thereto which when assembled forms an integral The inner anode member shown consists of a graphite or carbon cylinder 58 having openings 59 therethrough which provide communication when placed in position in a cell between the catholyte and anolyte compartments. The openings may be any shape but are usually circumferentially elongated slots spaced somewhat as shown, i.e., in vertically spaced rows in that portion of the anode which is below the electrolyte level. Both the distance between the slots circumferentially and the rows vertically are sufficient to retain good supporting strength in the member. The ratio of the area of the openings to the solid portion of the inner anode member is not critically important, b-ut the openings should be of sufficient area to permit passage therethrough of the electrolyte during electrolysis. The ratio of the area of the openings are usually between 30 and 60 percent of the total area of the inner anode area extending below the electrolyte level.

In FIGURE 4 is shown a sectional elevation of a cell of the invention employing a modified inner anode member 60 having specially modified slots 62 therein. The Slots are circumferentially elongated and arranged in vertical rows similar to those sho-wn in FIGURE 3 but in contrast thereto do not extend substantially horizontally through the inner member but are inclined upwardly therethrough into the exterior anolyte compartment to serve as a sort of trap to prevent substantially all the chlorine formed from either remaining in or returning to the catholyte compartment, Top plate 70 is an integral continuation of inner anode member 60, similar to 24 and 26 of FIGURES 1 and 2 but, in `contrast thereto, is not inte-gral with outer anode member 20 but merely makes electrical contact therewith, thus providing a -means for lifting out inner anode member 6i) together with cathode 32. Feed line 67 having valve 68 therein provides a means for continuous supply of electrolyte to container 16. Outlet 64 leading from 28 for gas and excess electrolyte leads to outlet 65 for gas and outlet 66- for electrolyte comprises a modification of outlet 50 of FIGURE 2. An enlarged fragmentary View of inner anode member 60 of FIGURE 4 is shown in FIGURE 5.

The electrolyte of the invention is a fused salt mixture consisting of l part -by Weight of an alkali metal uranous fluoride and between l and 2 parts by weight of an alkali metal chloride.

One mode of operation of the cell employing the electrolyte of the invention in a cell similar to that shown in FIGURE 1 of the drawing is to place NaCl in electrolyte chamber 3 in an amount sufficient to iill it to approximately 1/2 of its capacity. Burner 10 is lighted and the NaCl melted. An alkali metal uranous fluoride, e.g., NaUF5 or a mixture consisting chiefly of an alkali metal uranous uoride and balance NaCl, dependent upon the weight of NaCl already in the'cell, is then added to the molten NaCl to give a Weight ratio in the electrolyte of 1 of the alkali metal uranous fluoride to between 1 and 2 of NaCl. If desired, the proportions of NaCl and the alkali metal uranous fluoride may all be premixed before adding. Electrical lead lines 34 and 36 are then connected to a source of D.C. to effect electrolysis. The amperage is not critical, but is usually between 25 and 55 amperes, e.g., 50 amperes. In a -cell having an electrolyte chamber capacity of about 70 cubic inches, a voltage of between 3 and 6 volts is satisfactory.

As the electrolysis proceeds, uranium metal and chlorine gas are produced. The uranium metal, which collects on cathode 32, falls therefrom, and is deposited on bottom 18 of the cathode and the chlorine escapes through vent 38. The reaction thought to take place is represented by the equation:

NaUF5-|-4NaCl- U(metal) +2C12+5NaF Since both the alkali metal uranous fluoride andthe alkali metal chloride are gradually consumed during the electrolysis, fresh electrolyte must be added to the cell chamber. The alkali metal fluoride produced has a lower decomposition potential than the reactants, eg., NaUF5 or NaCl, and therefore forms a part of the electrolyte. As a result thereof, the volume of electrolyte increases and a portion thereof must be removed. The addition of fresh electrolyte may be done periodically as by removing cover 22 of FIGURE l or cover 54 of FIGURE 2 and adding it through the opening provided. The depleted electrolyte may be removed through the same openings by removing the covers and dipping or siphoning the excess out, or its removal may be provided for by overflow lines as shown by 50 in FIGURE 2 and by 66 in FIGURE 4. It is recommended that the ratio of NaCl to NaUF5 or KUF5 be greater than a weight ratio of 1:1 at all times, eg., a ratio of about 1 NaUF5 or KUF5 to 1.5 to 1.75 of NaCl.

The composition of the electrolyte during operation is ascertained by measuring the chlorine evolved and calculating the composition of the remaining electrolyte according to the above equation. The depleted electrolyte which is removed may be economically employed in the preparation of additional NaUF5 -by reacting it with UCI., according tothe equation:

The following example will serve to illustrate the operation of the cell of the invention.

A cell of the type shown in FIGURE 1 was used. Sufficient NaCl to ll chamber 16 to about 50 percent of its capacity was placed therein. Burner 10 was lighted and the NaCl thereby melted. Sufficient NaUF5 was then admixed with the molten NaCl in chamber 8 and melted to give a salt mixture having a ratio of NaUF5 to NaCl in the electrolyte of 1 to 1.5. The temperature of the electrolyte was maintained at between 800 and 850 C. Lead lines 34 and 36 were connected t0 the posit've and negative terminals, respectively, of a source of D.C., thereby effecting electrolysis in the fused salt bath according to the equation set out hereinabove. Uranium metal deposited on floor 18 of chamber 16 and C12 gas evolvedfrom vent 33. The amount of chlorine produced was measured to determine the bath composition. Current was maintained at an average of about 50 amperes; the potential varied between 3.5 and 6.0 volts. Electrolysis was continued for 70 minutes during which 188 grams of NaUF5 were electrolyzed. The uranium metal thus formed was removed from the cell and weighed and analyzed for uranium. 104 grams of uranium metal were produced which analyzed 99 percent uranium. This was a current efficiency of percent, based upon the following calculation: Since theolretically, the production of 238 grams of quadravalent U metal requires 386,000 coulombs and 99 percent of grams of 99 percent pure product or about 104 grams of U were produced, then theoretically,

and x=about 168,600 coulombs. Instead of 168,600 coulombs, however, 210,000 coulombs were required as produced by a current of 50 amperes for 4200 seconds (70 minutes). The current e'iciency, therefore, is:

The shape of the cell shown in the drawing is cylindrical and offers certain advantages over a cell of another shape. However, a cell having a rectangular or other poiylgonal shape is fully satisfactory for the practice of the invention.

Having described the invention, what is claimed and described to be protected by Letters Patent is:

1. An improved electrolytic cell for the production of uranium metal consisting of an impervious anode bottom; extending upwardly from the outer edges thereof a substantially impervious anode member forming the outer walls of the cell; a fluid-permeable anode inner member connected to said outer member by a substantially horizontal conducting plate and extending downwardly from said plate in a substantially parallel and spaced-apart relationship to said outer member to within between about 0.25 and 1.0 inch of said bottom to form an anolyte compartment between said inner and outer members and a catholyte compartment within said inner member; a gas vent in the upper part of said anolyte compartment; a metal cathode suspended in said catholyte compartment; and a means for supplying heat to said compartments.

2. The cell of claim 1, wherein said anode inner member is composed of porous carbon.

3. The cell of claim 1, wherein said anode inner member is composed of a material selected from the class consisting of graphite, carbon, tantalum, molybdenum, uranium, molybdenum-clad steel, and uranium-clad steel containing openings therethrough comprising between 30 and 60 percent of the area of said anode inner member which extends below the level of the electrolyte.

4. The anode inner member of claim 3, wherein said openings are horizontally elongated slots arranged in a series of vertically spaced-apart rows.

5. The anode inner member of claim 4, wherein the slots are sloped upwardly toward the anolyte compartment.

6. A cell for the production of uranium by electrolysis consisting of: a heating means; a chamber adapted to hold a fused salt electrolyte; a metal cathode suspended substantially centrally in said chamber; a two-member anode assembly spaced about said cathode as a center and consisting of an inner Huid-permeable member defining a catholyte compartment in the central portion of said chamber about said cathode, an outer impervious member extending in spaced-apart relationship and substantially parallel to said inner member to a level below said inner member and an impervious bottom integrally joining said outer member thereby defining an anolyte compartment in the exterior portion of said chamber between said inner and outer members having a continuous communicating passageway with said catholyte compartment -below said inner member, and a connecting electrically conducting plate connecting said inner and outer members at the top thereof; and an outlet for gas and liquid in said outer member leading from said anolyte compartment at a point near the top thereof.

7. The cell of claim 6, which has a tightly fitting insulating cover about said cathode over said catholyte compartment and a means for supplying a protective substantially unreactive gas in the zone above the electrolyte in said catholyte compartment.

8. The cell of claim 6, wherein the two-member anode assembly consists of two concentric cylinders, the outer member forming the Wall of an impervious electrolyte chamber, and the inner one, being permeable to fluids and of shorter length than said outer member forming an inner compartment and an outer annular compartment which have fluid communications therebetween.

References Cited in the ille of this patent UNITED STATES PATENTS 596,458 Inglis ec. 28, 1897 816,298 Lyons et al. Apr. 3, 1906 1,299,947 Ingeberg Apr. 8, 1919 1,486,546 Rhodin Mar. 11, 1924 1,842,703 Vorce Jan. 26, 1932 2,361,974 Smith Nov. 7, 1944 2,717,234 Nagy et al. Sept. 6, 1955 2,796,392 Lietzke June 18, 1957 FOREIGN PATENTS 481,071 Canada Feb. 12, 1952 UNITED STATES PATENT OFFICE CEERTHECATE 0F CORRECTION Patent No. 3,079,324 February 26, 1963 Donald R. Allen et al.

hat error appears n the above numbered patlt is hereby certified t 'that the said Letters Patent should read as ent requiring correction and corrected below.

Lyons et al.-Apr., 3, 1906" Column 6, line 33, for "816,298

read 816,928 Lyons et al.,---Apr. 3,

Signed and sealed this 14th day of January l964.,

(SEAL) tGSt EDWIN L. REYNOLDS ERNEST W., SWIDER Attesting Officer Acting Commissioner of Patents UNITED STATES PATENT oEEICE CERTIFICATE OF CORRECTION Patent No. 3,079,324 February 26, 1963 i Donald R. Allen et al.

t is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 33, for "8l6,298 Lyons et al.-Apr. 3, 1906" read 816,928 Lyons et al -Apr. 3, 1906 Signed and sealed this 14th day of January 19641 (SEAL) Attest: EDWIN L. REYNOLDS ERNEST We, SWIDER Attesting Officer Ac t ng Commissioner of Patents 

1. AN INPROVED ELECTROLYTIC CELL FOR THR PRODUCTION OF URANIUM METAL CONSISTING OF AN IMPERVIOUS ANODE BOTTOM; EXTENDING UPWARDLY FROM THE OUTER EDGES THEREOF A SUBSTANTIALLY IMPERVIOUS ANODE MEMBER FORMING THE OUTER WALLS OF THE CELL; A FLUID-PERMEABLE ANODE INNER MEMBER CONNECTED TO SAID OUTER MEMBER BY A SUBSTANTIALLY HORIZONTAL CONDUCTING PLATE AND EXTENDING DOWNWARDLY FROM SAID PLATE IN A SUBSTANTIALLY PARRALLEL AND SPACED-APART RELATIONSHIP TO SAID OUTER MEMBER TO WITHIN BETWEEN ABOUT 0.25 AND 1.0 INCH OF SAID BOTTOM TO FORM AN ANOLYTE COMPARTMENT BETWEEN SAID INNER AND OUTER MEMBERS AND A CATHOLYTE COMPARTMENT WITHIN SAID INNER MEMBER; A GAS VENT IN THE UPPER PART OF SAID ANOLYTE COMPARTMENT; A METAL CATHODE SUSPENDED IN SAID CATHOLYTE COMPARTMENT; AND A MEANS FOR SUPPLYING HEAT TO SAID COMPARTMENTS. 